His old friends like Brock and Misty could make a comeback. They might join Ash on parts of his journey and offer their own expertise. There could also be new characters, like a young trainer who idolizes Ash and follows him on his travels to learn from him.
Team Rocket might still be around, causing trouble for Ash as they always do. And there could be some powerful Gym Leaders or Elite Four members from different regions that play significant roles, either as allies or opponents to Ash during his travels.
Pikachu, of course. It's always been Ash's closest partner.
Perhaps Ash is on a quest to complete a special Pokémon research project this time. He travels through the regions, interviewing different trainers and Pokémon experts. He might get involved in some local Pokémon traditions and competitions that he hadn't experienced before. His Pikachu will surely be by his side, and they might develop new battle strategies against the diverse Pokémon they encounter.
He might meet some of his old friends again, like Brock or Misty. Maybe they will join him on his new journey through the regions.
It could be a new evil team that wants to control all the Pokémon for their own greedy purposes.
Brock could also be a main character. Since he has knowledge about Pokémon care and breeding, he could be Ash's colleague in the fanfiction. They could work together on projects related to Pokémon health and nutrition.
Maybe Ash will encounter new and rare Pokémon in the regions this time. He could also meet some old friends and have epic battles together.
A young girl named Mia might be a character too. She is also a Glacion fan and is very competitive. She challenges Ash to various Glacion - related challenges, like a Glacion knowledge quiz or a race to find a hidden Glacion item in the forest.
In this fanfiction, Gary could be an important character. Since he has always been in competition with Ash, he might have mixed feelings about Ash being the chosen one. Serena could also be a main character. She might be inspired by Ash's chosen - one journey and decide to follow him, offering her own skills and support. Professor Oak would likely be involved as well, guiding Ash with his vast knowledge of Pokémon.
Well, Pikachu could still be a main character. Even if Ash hates everyone, Pikachu might be the one trying to bring back the old Ash. Maybe Team Rocket could also be main characters. They are always around Ash, and his new - found hatred could make their interactions even more interesting. They might be confused by his change or even try to take advantage of it.
May could be one of the main characters. She could join Ash on his journey and share her knowledge about Hoenn's Pokemon with him. Another could be Brock, still tagging along to offer his expertise in Pokemon care.
Team Rocket might be main characters as well. They could be constantly trying to capture Ash or his Pokemon because of his special status. Their bumbling attempts to take advantage of Ash's link to Arceus could add a lot of comical and action - filled moments to the fanfiction. And of course, Arceus itself could be a major character, guiding Ash in some way or interacting with him directly.